Passive optical resonator with mirror structure suppressing higher order transverse spatial modes

Abstract

An optical resonator is designed to suppress higher order transverse spatial modes. Higher order transverse modes in the inventive optical resonator are forced to be unstable, and ultimately achieving single transverse mode resonator operation. Specifically, the mirror shape or intracavity lens profile is tailored to bound the lower order modes while rendering the higher order modes unstable. This has application in MEMS/MOEMS devices by reducing side mode suppression ratio (SMSR) dependence on alignment tolerances, for example.

What is claimed is:  
     
       1. An optical resonator comprising at least one optical cavity defined by at least two mirror structures in which          V   r     ≡         π                 w     λ          n   _              d   0     /     L   c                           
       is less than about 3.5; where d 0  is a sag of a net mirror profile of the mirror structures and w is a full width at half maximum (FWHM) diameter of the net mirror profile of the mirror structures, {overscore (n)} is the refractive index of the optical cavity; λ is the wavelength of operation, and L c  is a length of the optical cavity. 
     
     
       2. A resonator as claimed in  claim 1 , wherein V r  is less than 2.8. 
     
     
       3. A resonator as claimed in  claim 1 , wherein V r  is less than 1.5. 
     
     
       4. A resonator as claimed in  claim 1 , wherein in an optical distance between the mirror structures is tunable. 
     
     
       5. A resonator as claimed in  claim 1 , wherein an optical distance between the mirror structures is tunable by out-of-plane deflection of one of the mirror structures. 
     
     
       6. A resonator as claimed in  claim 1 , wherein a first one the mirror structures is relatively flat such that d 0  and w are based on the mirror profile of the second mirror structure. 
     
     
       7. An optical resonator having an optical cavity defined by a first mirror structure comprising a substantially flat surface on which a first dielectric mirror is deposited and a second mirror structure comprising a curved surface on which a second dielectric mirror is deposited, wherein a ratio of the mode 1/e 2  intensity of a lowest order mode to the full width at half maximum (FWHM) diameter of the curved surface of the second mirror structure is greater than 0.7. 
     
     
       8. A resonator as claimed in  claim 7 , wherein the ratio is greater than about 1. 
     
     
       9. A resonator as claimed in  claim 7 , wherein the ratio is greater than about 1.2. 
     
     
       10. A resonator as claimed in  claim 7 , wherein in an optical distance between the mirror structures is tunable. 
     
     
       11. A resonator as claimed in  claim 7 , wherein at least one of the mirror structures is formed on an electrostatically deflectable structure. 
     
     
       12. An optical resonator comprising at least one optical cavity defined by at least two mirror structures in which          3.5   >         π                 w     λ          n   _                         d   0     /     L   c             ;                   
       where d 0  is a sag of a net mirror profile of the mirror structures and w is a full width at half maximum (FWHM) diameter of the net mirror profile of the mirror structures, {overscore (n)}is the refractive index of the optical cavity; λ is the wavelength of operation, and L c  is a length of the optical cavity.